Vacuum-indicator.



G. F. GRAY.

VACUUM INDICATOR.

APPLICATION FILED SEPT. 7, 1912. RENEWED FEB. 23. 1915.

1,154,306, Patented Sept. 21, 1915.

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UNITED STATES PATENT orrrcu.

GEORGE E. GRAY, OF SCHENECTADY, NEW YORK, ASSIGNOR T0 GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

VACUUM-INDICATOR.

Specification of Letters Patent.

Patented Sept. 21, 1915.

Application filed September 7, 1912, Serial No. 719,191. Renewed February 23, 1915. Serial No. 10,121.

To all whom it may concern:

Be it known that L-GEORGE F. GRAY, a citizen of the United States, residing at Schenectady, in the county of Schenectady, State of New York, have invented certain new and useful Improvements in Vacuum- Indicators, of which the following is a specification.

My invention relates to spark gap protective devices of thevacuum type, commonly known as vacuum lightning arresters, in which electrodes spaced apart to form a spark gap are mounted in a chamber exhausted to such an extent that the gap will break down and form a discharge path at much lower voltages than it would in air at atmospheric pressure. If by accident, leakage or otherwise the vacuum is impaired, the pressure in the chamber rises and the breakdown voltage of the arrester likewise rises. If the vacuum is entirely lost the breakdown voltage becomes so much higher than normal that the system is left practically without protection. As the loss of vacuum produces no visible change in the appearance of the arrester considerable difficulty is met with in locating those arresters which have lost their vacuum.

The purpose of my invention is to facilitate detection of defective arresters, and to this end I provide means whereby a loss of vacuum automatically causes such a marked decrease in the resistance of the arrester that the defective arrester may easily be detected by some simple test. One way of causing the desired decrease in resistance is which my invention may be embodied, and

in which Figure 1 is an elevation of a form of vacuum lightning arrester in which my invention may be embodied; Fig. 2 is a longitudinal section through the arrester shown in Fig. 1, showing the automatic bridging arrangement in elevation; and Fig. 3 is a longitudinal section of the automatic means by which the electrodes are bridged.

In the particular form of arrester shown in the drawing a porcelain base 1 carries a vacuum arrester having an evacuated metal vessel comprising a metal tube 2 which is connected to ground near the middle through a suitable ground connection 3. The metal tube is closed at both ends and is exhausted to any suitable degree of vacuum. Electrodes mounted in the tube to form spark gaps to ground are connected to line through end terminals 4. As long as the vacuum in the metal vessel is of the proper value the arrester will discharge to ground at a voltage slightly above normal. If for any reason the vacuum is badly impaired or lost, the discharge voltage is raised very appreciably and the arrester should be replaced.

The construction of the arrester will best be understood by referring to Fig. 2, which shows in section the evacuated metal vessel containing disk electrodes 5 mounted .concentric with the metal tube and spaced awav from the tube to form spark gaps 6 through which discharge from either electrode 5 to ground can occur. Each electrode is supported on a porcelain electrode support 7 and is provided with a leading-in wire 8 which extends longitudinally of the tube through a suitable seal, preferably consisting of a stopper 9 made of porcelain or similar material which does not impair the vacuum when heated and backed up by viscous wax 10 which in turn is held in place by an,.insulatitng end piece 11, through which the leading-in wire 8 extends to make electrical connection with the terminal 4. lVhen an abnormal voltage occurs on the line a discharge takes place from the electrodes 5 through the spark gap 6 to the metal tube 2 and thence to ground.

In accordance with my invention, the electrodes 5 are automatically bridged and the resistance of the arrester reduced to practically zero by a suitable automatic (lQX'iCG responsive to variations in pressure in the evacuated chamber. In the preferred construction the electrodes 5 are connected through wires 12 to contacts 13 of the automatic bridging device. The contacts 13 are spaced apart such a distance thatunder normal conditions their discharge resistance is much greater than the discharge resistance of the spark gap 6 so that there is no tendency for discharges to take place between the contacts 13 during normal operation of the device. These contacts extend into a substantially closed chamber 14 having only a capillary opening 15, as best shown in Fig. 3. This capillary opening is normally scaled y ubody of mercury .16 contained in any suitable receptacle, preferably a bulb shaped receptacle 1? made of glass or other suitable :material. 'lhechamber lll is evacuated to the same degree of vacuum as the metal vessel of the arrcstcr and as long as the vacuum in the metal vessel is normal the chamber 14 is empty, as shown in Fig. The bulb or receptacle 17 is open to the interior of the metal tube 2 preferably through capillary openings which will prevent the mercury in the bulb to respond to variations in pressure in the tube, but which willalso prevent spilling of the mercury. In the particular arrangement shown, the bulb 17 is secured to the chamber 14: by a porous cement 18 traversed by numerous capillary openings which permit the pressure of the residual gases in the evacuated vessel to bc'exerted upon the surface of the mercury 16. By placing the capillary opening 15 of the chamber 14 in the position shown, near the center of the bulb shaped receptacle 17, the capillary opening is always sealed by the mercury in which it is submerged so that the device will operate regardless of the position of the arrester. In order that the heat of the discharge through the spark gaps 6 may not afiect the automatic bridging device,

shields 19 of some suitable refractory ma terial are placed, as shown in Fig. 2, between each electrode and the automatic bridging device.

The operation of the device is as follows: lVhen the vacuum in the arrester is normal the mercury is in the position shown in Fi". 3 and the chamber 1 1 is empty. If for any reason the vacuum in the arrester is impaired or lost, the increase in pressure of the residual gases in the metal vessel is transmitted through the capillary openings in the cement 18 to the mercury 16 and forces the mercury through the capillary opening 15 into the chamber 14, whereupon the contacts 13 are bridged by the mercury, the electrodes 5 are placed in electrical connection, and the resistance of the arrester becomes so low that the defective arrester may easily be detected.

My invention may be embodied in many other forms than that shown and described and I therefore do not limit my invention to the precise arrangement disclosed except in so far as it is limited by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States 1s 1. The combination with an evacuated vessel containing electrodes, of means for holding a body of mercury in said vessel exposed to the pressure in said vessel, and

means responsive to the increase in pressure due to impairment of the vacuum in said vessel for bringing said mercury into electherein and spaced away from the walls of said vessel to form spark gaps, of contacts connected to said electrodes and mounted to form between them a discharge path of greater resistance than said spark gaps, and means responsive to abnormally high pressure in said vessel for electrically connecting said contacts.

4. The combination with an evacuated vessel containing electrodes, of a receptacle in said vessel containing a mobile conducting liquid exposed to the pressure of the residual gases in said vessel, an evacuated chamber having a capillary opening submerged in said conducting liquid, and means whereby the entrance of said conducting liquid through said opening into said chamber electrically connects said electrodes.

5. The combination with an evacuated vessel having electrodes therein, of a bulb containing mercury exposed to the pressure in said vessel, an evacuated chamber secured to said bulb and having a capillary opening to said receptacle near the center of said receptacle, and contacts electrically connected to said electrodes and mounted in said chamber in position to be bridged by mercury forced from said receptacle into said chamber through said opening by increase in pressure in said vessel.

6. The combination with an evacuated vessel having electrodes therein, refractory shields mounted between said electrodes and separated to leave a space between them, and means mounted in said space for automatically connecting said electrodes electrically in response to increase in pressure in said vessel.

7. The combination with an evacuated vessel comprising a metal tube closed at the ends and disk electrodes mounted in said tube and spaced away from the walls of said tube to form spark gaps, of insulating shields spaced apart between said electrodes,

brought into electrical connection with both of the electrodes upon an increase of pressure in said vessel.

8. An automatic indicator for Vacuum arresters comprising a receptacle containing mercury, a substantially closed chamber having a capillary opening submerged in the mercury in said receptacle, and contacts in said chamber mounted in position to be lbridged by mercury forced into said cham- 9. An automatic indicator for vacuum arresters comprising a bulb shaped receptacle containing mercury and having capillary openings in its walls, a substantially closed chamber secured to said receptacle and communicating with said receptacle through a capillary opening near the center of said receptacle, and contacts in said chamber bridged by mercury forced into said chamher through said opening. 7

10. The combination with an evacuated vessel having electrodes mounted therein, of contacts electrically connected to said electrodes, and means inclosed in said vessel for bridging said contacts upon increase of pressure in said evacuatedvessel.

11. The combination with an evacuated vessel having electrodes mounted therein, of a bulb containing a fluid responsive to pressure in said vessel, an evacuated chamber secured to said bulb having an opening into said bulb below the surface of said fluid, and contacts electrically connected to said electrodes and mounted in said chamber, said contacts being bridged in response to flow of said liquid into said chamber. Y

In witness whereof, I have hereunto set 'my hand this 5th day of September 1912.

GEORGE F. GRAY.

Witnesses:

BENJAMIN B. HULL, HELEN ORFORD. 

